In order to monitor information inside a tire, such as an internal pressure and temperature, there has been heretofore performed attachment of a sensor device to a well part of a rim, detection of the information inside the tire by use of the sensor device, and transmission of the detection results to a receiver outside of the tire by utilizing radio waves.
In such a sensor device for a tire, generally, a sensor and a transmitter are mounted on a printed board, a transmission antenna is printed on the printed board, and these sensor and transmitter are housed in a thin case together with the printed board.
Upon attachment of the sensor device described above to a well part of a rim, assembly of the rim is not disturbed by the sensor device if a bottom of the case is allowed to follow a surface of the well part. However, as described above, most sensor devices include the antenna printed on the printed board. Thus, if the printed board is disposed parallel to the well part, there is a problem that transmission efficiency is extremely deteriorated. Consequently, in the present circumstances, the sensor device is attached so as to allow the printed board to stand against the well part of the rim, and instead, lowered workability of the assembly of the rim is accepted. Moreover, there has been proposed a sensor device in which a transmission antenna is protruded to the outside of a case. However, also in this case, lowered workability of assembly of a rim is inevitable (for example, see Japanese patent application Kohyo publication No. Hei 10(1998)-504783).